In general, a control server based IPv6 over IPv4 transition method is a method (referred to as RFC 2529 and RFC 3053) of creating a control tunnel to the control server in order to enable a service terminal to register its service in the control server and require converted address information on a terminal to be communicated. An IPv6 terminal requires an IPv4 address that can communicate with an IPv6 address of a reception terminal (the other side) from the control server by using the created control tunnel and obtains the IPv4 address. Each terminal transmits a tunnel creation request message to the control server in order to initially create a control tunnel so as to be registered in the control server, so that the aforementioned information can be managed.
As conventional methods for IPv6 over IPv4 transition, there are translation methods and server based transition methods.
The translation method is a method in which a network address translator is provided between two different IP version networks to enable IPv6 and IPv4 connection. In this method, address translation has to be performed on all packets, so that there is a problem of extensibility.
The server based transition (IPv6 over IPv4 transition) methods may be classified into tunnel broker (referred to as RFC 3053), Teredo, and intra-site automatic tunnel addressing protocol (ISATAP).
The tunnel broker is a device for relaying tunnels, and a terminal in an IPv4 network creates a tunnel to a gateway between the IPv4 and IPv6 networks. Here, the control tunnel is created to enable a terminal in the IPv4 network to register its own information in a server to communicate with a terminal in the IPv6 network, and acquire information to communicate with a terminal on the other side.
Next, Teredo uses a method similar to the tunnel broker method but is not assigned officially by the Internet assigned numbers authority (LANA). However, in this method, a prefix for Teredo is defined additionally, and a protocol is designed to include a possibility in which a terminal in the IPv4 network is under the network address translation (NAT). However, the tunnel broker method describes a general structure in the RFC 3063 but is practically implemented in consideration of address translation, so that the Teredo and the tunnel broker method are not much different from each other. In addition, since Teredo can extract an IPv4 address from an IPv6 address, terminals can directly communicate with each other without passing through a device such as a Teredo relay, and this is a difference between the two methods.
The ISATAP is an automatic tunneling method used between terminals or between a terminal and a router to provide communications between a terminal in an IPv4 intranet and another terminal in the same intranet or a terminal in an IPv6 public network connected to the intranet. This method is a protocol that is not standardized by RFC yet but basically provided in Microsoft Windows operating systems. ISATAP addresses use the interface identifier ::0:5EFE:w.x.y.z, in which w.x.y.z is an IPv4 address. The ISATAP interface identifier can be combined with any 64-bit prefix that is valid for IPv6 unicast addresses.
As described above, the ISATAP address includes IPv4 source and destination addresses used to transmit ISATAP traffic through an IPv4 network such as an IPv4-compatible address, a 6 over 4 address, and a 6 to 4 address.
However, the aforementioned general IPv6 over IPv4 transition method has problems in that as the number of service terminals increases, the number of control tunnels increases, and a control server has loads of tunnel management. This is because the control server measures a lifetime of each control tunnel and deletes or maintains the control tunnel after a service from a terminal is terminated. In addition, the control server enables forwarding to transmit data to the terminal to be communicated through the control tunnel. As described above, maintaining the control tunnel and data forwarding through the control tunnel may cause degradation in performance of the control server.